Conventional prior art fuel injectors feature a hydraulic needle valve which is activated to inject fuel into the combustion chamber of the engine. In activation of the needle valve, a volume of fuel does not reach the combustion chamber but instead is circulated back through the fuel injector—there may also be a flow channel permanently available for circulation back of a proportion of the fuel. This returned volume of fuel is conventionally referred to as “back leak” fuel, and introduces several technical issues, discussed below, which degrade the performance of the prior art fuel injectors.
Typically, a fuel injector includes an injection nozzle having a nozzle needle which is movable towards and away from a nozzle needle seating so as to control fuel injection into the engine. The nozzle needle is controlled by means of a control valve, which controls fuel pressure in a control chamber for the nozzle needle. Typically, opening the control valve decompresses the control chamber, which consequently opens the injection nozzle and fuel is injected into the combustion chamber. During decompression of the control chamber, a volume of fuel, which is required to maintain the pressurised environment within the control chamber when the control valve is in a closed state, is ejected as a back leak fuel flow from the fuel injector.
This back leak fuel flow may be at a very high pressure and temperature. Often the pressure may be of the order of hundreds of bar, or depending on the application can even reach thousands of bar (e.g. up to 2500 bar in some designs). As a result of these extreme pressures several issues arise during the operation of the fuel injector, which deteriorate the performance of the fuel injector.
Typically, prior art solutions involve the drilling of one or more conduits within the fuel injector body, providing one or more channels along which the back leak fuel may be evacuated from the control chamber, and returned to the fuel management system for use in a subsequent combustion cycle. By fuel management system is intended the plurality of apparatus required to deliver fuel to the fuel injectors, which comprises the fuel tank, the assortment of pumps required to direct fuel to the fuel injectors, and the electronic control unit (ECU) which monitors the engine performance, and ensures the required volume of fuel is delivered to each fuel injector. Managing the back leak fuel flow in the manner described above introduces several problems, which over the course of time lead to a deterioration in the performance of the injector.
One problem commonly associated with back leak fuel flow is that of general wear to the surrounding apparatus, and in particular wear within the back leak flow channel, due to the volume and the high pressure of the back leak fuel flow passing through the channel over time. These problems are exacerbated by the formation of deposits and other sediment, which tend to coagulate within the one or more channels.
The back leak flow conduit is typically a bore of narrow diameter machined within the body of the fuel injector. The machining of the back leak flow conduit presents significant difficulties during manufacture due to the relative small diameter of the injector body and the material of the body. Often the injector body is comprised of several different components with the back leak channel running through the components. This requires a very high and accurate level of machining to ensure that the back leak channel is perfectly aligned in each of the components. Accordingly, the specialised nature of the machining work required contributes significantly to the production cost.
Alternative back leak channel designs are disclosed in WO 2009/023887 (corresponding to U.S. Patent Application Publication 2011/0186647), EP 1130249 (corresponding to U.S. Pat. No. 6,279,842), and DE 10 2007 011789 (corresponding to U.S. Patent Application Publication 2010/0102143). WO 2009/023887 discusses the use of unpressurized fuel to flush an injector assembly, and EP 1130249 shows a magnetostrictive rod controlled injector in which some fuel is allowed to leak for cooling purposes through the injector assembly.
Currently, all the major components housed within a fuel injector are purpose-built for the injector in which they are to be used, and components built for use in one model and/or size of fuel injector are not cross-compatible for use within different fuel injectors, due to the different dimensions of the fuel injectors, and therefore the different dimension of required component. This lack of cross-compatibility is a serious issue for manufacturers of fuel injectors, in so far as separate production lines of component are required for each different model of fuel injector, inevitably increasing production costs and time.
It is an object of the present invention to resolve the aforementioned issues commonly associated with prior art fuel injectors.